Heretofore, in an optical communication executed using an optical fiber, a ferule 43 for an optical connector is used to connect optical fibers 42 to each other as shown in FIG. 6. The ferule 43 optically connects the optical fibers 42 to each other by fixing and holding the optical fibers 42 therein and inserting them from both the sides of a sleeve 41. Further, the ferule 43 employs such a structure that the portion thereof engaged with the sleeve 41 is covered with a pipe of metal and the like for the purpose of accuracy and reinforcement.
Note that the ferule for the optical fiber that are practically used at present is mainly of a SC type (Single fiber coupling optical Connector) and the like in which the portion of the ferule engaged with a sleeve is have an outside diameter of 2.5 mm and of a MU type (Miniature-Unit coupling optical fiber connector) and the like having an outside diameter of 1.25 mm, the SC type ferule having the outside diameter of 2.5 mm becomes a standard model in the world, and, in recent years, a demand for the ferule having the outside diameter of 1.25 mm is increased.
A ferule 50 shown in FIG. 7 is disclosed as the structure of the ferule covered with the pipe of metal and the like (Japanese Examined Patent Publication No. 5-23402). The ferule 50 includes a molded resin covered with a metal pipe 51 to which a concavo-convex portion 52 having a different diameter is formed. The adhesive force of the ferule 50 with a molded resin is increased by the concavo-convex portion 52, thereby the extraction of the metal pipe can be prevented.
Further, a ferule using a hard member 62 having a through-hole 61 is disclosed as shown in FIG. 8 (Japanese Patent Application Laid-open Publication No. 7-168054). In this ferule, a resin injected from an injection port is supplied into a hollow portion that forms a collar 63 and further into the inside of the hard portion 62 passing through the through-hole 61. The extraction of the hard member 62 can be prevented by molding the resin filling the through-hole 61 as described above.
Incidentally, in the structure in which the concavo-convex portion is formed to the metal pipe, complex processing is required to form the concavo-convex portion, and there is a worry that when the resin is molded, the concavo-convex portion of the pipe makes the flow of the resin bad and works against the filling of the resin. Further, an effect for preventing the rotation of the pipe cannot be obtained in the concavo-convex portion. Further, since the pipe is formed differently in front and rear portions, a step for discriminating the front portion from the rear portion to automatically execute a working process.
In contrast, in the structure in which the metal pipe has the through-hole through which the resin passes, particularly when the metal pipe has a small diameter, a fine hole is formed as the through-hole, which makes the flow of the resin bad. Further, the resins, which have passed through a plurality of holes, are mixed with each other to thereby form a welded layer of the resin in the vicinity of the extreme end of the ferule, and thus there is a possibility that the resin cannot be molded well.
Further, when the metal pipe is attached to a metal mold, the position of the through-hole must be detected first and then the through-hole must be disposed in the metal mold in a predetermined direction. A sophisticated device is required to automatically detect the position of the through-hole, from which a problem arises in that the automation of the working process is prevented by the necessity of the device. In the manufacture of the products such as the ferules which are manufactured in a large scale, the automation of a manufacturing process is a very important problem.
Further, when the ferule is inserted into and extracted from the sleeve, a force of a lengthwise direction is applied to the pipe, whereas when the ferule is engaged with the sleeve, a force may be applied to the pile in a direction in which the pipe is rotated. Accordingly, it is not preferable for the pipe itself to rotate.
An object of the present invention, which was made in view of the above problems, is to provide a ferule for an optical fiber that can fix and mold a pipe favorably as well as can be manufactured easily.